1. Field of the Invention
The present invention relates to an electron beam recording apparatus and the beam adjustment method and, more specifically, to an electron beam recording apparatus and the beam adjustment method therefor that uses the electron beam to manufacture a master of a high-speed-rotating recording medium such as magnetic disk.
2. Description of the Related Art
A beam recording apparatus performs lithography using an exposure beam such as electron beam and laser beam, and is widely used in an apparatus for manufacturing a master of a large-capacity disk, e.g., optical disk including digital versatile disc (DVD), Blu-ray disc, or others, and a magnetic recording medium such as a hard disk.
In such a beam recording apparatus, a resist layer is formed on the recording surface of a substrate which is to be a master for manufacturing the disks exemplified above. The beam recording apparatus then rotates and translates the substrate to direct, as appropriate, a spot beam to the recording surface in, relatively, the radial and tangential directions. Using a spot beam as such, the beam recording apparatus performs control to form a latent image on the resist layer with a spiral or concentric track rendered on the recording surface of the substrate.
In such a beam recording apparatus, however, rotation runout occurs depending on the mechanical precision of a transfer motor, a spindle motor, and others, rotating and translating the substrate, and the rotation runout reduces the precision of track formation. It is needed to take some correction for such rotation runout during beam exposure or recording.
The rotation runout of a disk substrate includes, as is well known, synchronous runout (synchronous rotation runout) and asynchronous runout (asynchronous rotation runout). The synchronous runout is of a runout component in synchronism with the rotation frequency of a turntable, i.e., substrate, and the asynchronous runout is not dependent on the rotation frequency of the turntable, i.e., substrate, and occurs irregularly.
About the asynchronous rotation runout, Patent Document 1 (Japanese Patent Application Kokai No. H09-190651, page 4, FIG. 1) describes the correction technology in an exposure apparatus for an optical disk master, for example. The technology in Patent Document 1 is for correcting the problem of asynchronous rotation runout with an object of improving the track pitch accuracy, i.e., relative position accuracy with adjacent tracks, in the exposure apparatus for an optical disk master.
Unlike the asynchronous rotation runout, although reducing the roundness accuracy of the track, i.e., absolute accuracy, the synchronous rotation runout does not affect the track pitch accuracy. With an optical disk, because the roundness error caused by the synchronous rotation runout can be followed by a tracking servo of a disk reproducing apparatus, the synchronous rotation runout has not been perceived as a problem that much as the asynchronous rotation runout. However, there is the recent demand for creating a magnetic recording medium using an electron beam exposure apparatus because of the high recording densities of a hard disk being the magnetic recording medium. The magnetic recording medium is the one called discrete track medium or patterned medium.
The hard disk is high in rotation speed at data recording and reproduction, and the control band is narrow in a swing-arm control mechanism for use to perform track control over the recording reproducing head. The disk medium is thus strictly required to be high in track roundness accuracy. As such, the master exposure apparatus for manufacturing such a disk medium has to be capable of correcting, with high accuracy, not only asynchronous rotation runout but also synchronous rotation runout.
Patent Document 2 (Japanese Patent Application Kokai No. 2003-317285, pages 7 to 8, FIG. 3) and Patent Document 3 (Japanese Patent Application Kokai No. 2003-36548, page 8, FIG. 6) describe the technology for correcting both asynchronous rotation runout and synchronous rotation runout. With the technology, the recording beam position is controllably corrected based on information being an earlier measurement result about the displacement of a turntable in the radial direction.
In the Patent Document 2 is, for example, it is described about the technology for performing control over (correcting) the position to which a recording beam is irradiated based on the computation result of a displacement difference between reference displacement and radial displacement of a turntable. The reference displacement is in the radial direction and measured with a predetermined rotation speed or slower. The radial displacement is the displacement in the radial direction measured in real time during beam exposure. In this method, however, used as a reference is the displacement at the low rotation speed on the assumption that the synchronous component of the rotation runout is small at the low rotation speed, and the synchronous component is increased in proportion to the increase of the rotation speed.
The problem here is that the rotation synchronous component cannot be neglected even at low-speed rotation, and the rotation synchronous component is not necessarily increased in proportion to the increase of the rotation speed. As such, with the above methods, there is no way of knowing the synchronous rotation runout component observed during the rotation of capturing a reference displacement waveform, and thus no runout correction is possible.
In order to keep up with the high recording densities of a magnetic recording medium, e.g., discrete track medium or patterned medium, rotated at high speed for data recording and reproduction, there needs to correct not only the asynchronous rotation runout but also the synchronous rotation runout with considerably high accuracy. That is, the previous correction methods do not serve well enough for the synchronous rotation runout in such a magnetic disk or others, and no true rotation synchronous component can be completely corrected thereby. Such problems and objects have not been recognized.